DE19701320A1 - Method of controlling drive shaft of motor vehicle with internal combustion engine - Google Patents

Abstract

The accelerator pedal movements is monitored by a desired value transmitter which are then analysed by a computer. The engine is controlled with the aid of the computer, after each positive accelerator movement which results in a progressive engine power. If no drive slip-adjustment gearing exists, the engine is immediately guided to that torque with which at the instantaneous engine speed, a definite engine power is reached.

Description

The invention relates to a method for controlling a drive train of a motor vehicle with an internal combustion engine, with a continuously variable transmission and an accelerator pedal, the one Setpoint generator is assigned, wherein accelerator pedal movements with the setpoint generator monitored and analyzed in a computer to which a memory is assigned, whereby the driver program is adapted to the driver and situation. Such a process is z. B. from ATZ 1994, Issue 6, page 381 and ATZ 1994, Issue 10, page 584 known.

Internal combustion engines set their maximum output only at high engine speeds a narrow speed band available. They achieve the optimal efficiency on the other hand at medium speeds with high torque. A continuously variable transmission with large Gear ratio range is therefore optimal to be high at all driving speeds Engine performance for the best driving performance on the mountain and during acceleration to provide, and in the important part-load range with constant speed in the most frequent speed speed range between 100 and 150 km / h to ensure optimal engine efficiency.

For the small cars that are currently with continuously variable CVT transmissions in some automotive plants roll off the assembly line in very modest numbers, however, the gain in engine Efficiency compared to manual transmissions due to loss of efficiency in the transmission overcompensated. The acceleration time is longer, the maximum speed is lower and that Consumption higher than for cars with manual transmissions.

With a 2nd generation CVT version, the gearbox efficiency is now, for example by using a radial piston pump with throttling on the suction side and a load-dependent control of the contact pressure of the variator discs, improved. By using a hydrodynamic converter with slip-controlled lock-up clutch will maximum torque increased by a factor of 2. The larger spread becomes a larger one consumption-optimized overdrive range possible. The realization of a third CVT Generation with a special arrangement called "geared-neutral" Power split is now conceivable thanks to the electronic control options.

With a large overdrive range, for example approx. 60 to 70 km / h at 1000 rpm, you can the diesel engines in the partial load area, with low to medium speeds, at constant speed in most common speed range, between 100 and 150 km / h, largely in Best consumption area run.

The spontaneous performance necessary for special situations and desired by the driver unfolding, but is only from - unfavorable - partial load ranges in the higher Speed range possible. This is the conflict of objectives when controlling the CVT gearbox.  

So far, various driving programs have been implemented with an adaptive change in the characteristic curve, cf. e.g. B. W089 / 03319 (or US-5 113 721 A) and ATZ 1994, booklet, 6 page 381, depending on the driving situation and personal driving style, different with similar accelerator pedal positions Gear ratios enabled. Through a driver and situation-related adaptation a corresponding driving program is called up by the computer in order to either more the spontaneous performance desired by the driver and corresponding to the traffic situation possibility to increase, or to meet the consumption-optimized operating point adjustment.

However, changing traffic situations and driver requests are not for the computer predictable. It is therefore not possible to select a driving program that corresponds optimally. So far Most of the time, optimal consumption minimization has to be dispensed with in order to delay Prevent performance increase. The previous compromises cost fuel. Moreover A constant change of driving programs creates an unsafe feeling for the driver Gear behavior.

It is now the aim of the invention, the control algorithm for the drive train Motor vehicle, in particular with a continuously variable transmission as stated at the beginning to improve that even with a largely consumption-optimized control of the engine in Best range of the engine map, for example, that when driving through a column again and again necessary minor changes in performance, immediately, before or during the Speed change, by temporarily raising or lowering the Motor torque is made possible by the computer. Furthermore, if larger Increases in performance are predictable, the driver tapping the speed level ahead of the accelerator pedal can raise accordingly before a performance jump. The today usual, adaptive shifts of the operating characteristic according to personal driving style, to those for spontaneous power delivery over necessary, but low fuel consumption over longer periods should thereby largely avoided or at least very significantly be reduced. This enables significant fuel savings to be achieved.

This goal is achieved by the measures specified in claim 1; beneficial Refinements and developments are the subject of the dependent claims. In which Control algorithm according to the invention is new that progressive with the accelerator pedal path increasing until the maximum power, the engine power is determined. In stationary case at The computer controls constant travel as soon as a minimum accelerator pedal position and driving speed is exceeded and the traction device does not intervene Engine torque on the, in the engine map at the respective engine speed, consumption optimal torque. The gear ratio is calculated by the computer for the respective Driving speed determined so that together with the optimal consumption torque the engine power determined with the accelerator pedal division is achieved.  

With a positive accelerator pedal movement to increase performance, for example to trigger of an acceleration process, this is immediately during the translation change Engine torque raised by computer if necessary to the maximum possible. This is supposed to speed up the engine performance, even during the change in gear ratio, with the Accelerator pedal position determined higher output after the change in gear ratio, with which then higher speed and then the optimal engine torque again, correspond.

With a negative accelerator pedal movement to reduce the power during the over Settlement changes the engine torque from the computer so that the engine power immediately to the lower output corresponding to the new accelerator pedal position, with which then later lower speed and the again optimal fuel consumption, is reduced.

By briefly tapping the accelerator pedal, the driver can predict the engine speed raise to a higher speed level desired by him. When accelerating later a high level of performance is then immediately available for an acceleration process Available. Such a very short pressure increase on the accelerator pedal (tapping) interpreted the computer as a downshift command, but at the same time lowers the engine torque so far from that the engine power remains unchanged for the time being.

The level of the speed increase can be achieved, for example, by pressing the accelerator pedal reached reversal point of the accelerator pedal movement can be determined. The driver can do it orientate on the inhibition threshold.

In special cases, for example for a low speed overtaking heavy oncoming traffic, is a spontaneous acceleration at any time after tapping available. The loss of time when shifting down by two gears is also the case with the previous ones Automatic transmissions repeatedly criticized. The driver of a car too Manual transmission shifts down prematurely as soon as it believes an overtaking is about to take place to initiate. The possibility of lightly tapping the accelerator pedal Increasing the speed of a vehicle with a CVT transmission is therefore certainly sensible and not only psychologically important.

An optical, acoustic, but preferably a tactile signal on the accelerator pedal, such as vibration of the pedal, for example, does not remind the driver of a longer duration necessary speed increase that the engine is currently having an adverse effect right now The tactile signal is suppressed if the longest gear ratio has already been used is reached, or when the computer compares one with given parameters special driving condition, for example an ascent with a strongly changing power requirement, recognizes.  

This prevents long speed increases with excessive consumption. While possibly an optical signal always indicates excessive engine speeds, by tapping again Speed increase updated and the tactile signal thereby for a further period of time suppressed. With an accelerator pedal movement or power request in which the preselected speed is approximately reached or exceeded, or by a The speed increase is canceled from zero throttle position. The speed reduction can also as it is state of the art, depending on parameters, e.g. B. when winding uphill, be delayed. However, the engine output always corresponds to the new accelerator pedal position.

The tactile signal is only activated when the speed is increased for a longer period, and can therefore be felt relatively rarely. Since it is also at all times through a subconscious driving pedal movement can be eliminated immediately, it is hardly an unpleasant nuisance, but perceived as intelligent protection against unnecessary fuel consumption will.

The engine speed is the best point in the consumption map of the engine by a Inhibition threshold marked on the accelerator pedal path for the driver. In the vicinity of this Accelerator pedal position, the engine runs in the absolutely optimal best area of the engine map. This area in the engine map should therefore be used for acceleration processes in city traffic and when driving constantly on the highway, preferably used. The drivers will out of self-interest mostly approximates to that due to the accelerator pedal threshold Hold the recommended accelerator pedal position.

If a minimum vehicle speed is exceeded, an accelerator pedal Zero setting from the computer a fuel cut-off. The gear ratio is simultaneous controlled by the computer so that the engine only runs at the lowest possible speed. So be the losses due to the drag torque when rolling over a wide speed range minimized. This gives the driver the opportunity to start from a minimum speed City traffic and on winding country roads, depending on the respective traffic situation, by intermittent acceleration (pulse driving), similar to the momentum automatic control to save fuel.

Automation of this pulse method is also possible. Through a technical The cruise control can refine the drive at lower speeds Switch on and off intermittently for optimum consumption so that the specified speed only is exceeded or fallen below by a certain value. For minimizing consumption however, the driver's intervention remains more important. Only the driver can, far more intelligently as the computer, switch off the drive with zero gas far before an obstacle.

The invention will be exemplified below with reference to the drawing explained further. Show it:

FIG. 1 shows an example of a stored in the computer memory characteristic speed or engine power via the accelerator pedal path;

FIG. 2 shows an example of an engine map, likewise stored in the memory, which illustrates the relationship between power (or engine torque) and speed, specifying a working line for the minimum specific consumption; and

Figs. 3 to 6 show various diagrams in vehicle acceleration Examples of the application of the inventive technique.

In Fig. 1, line 1 shows the assignment progressively increasing the motor power in kW on the accelerator pedal path S (in percent). The accelerator pedal travel does not control the torque as before, but the engine output directly. For the speed (rpm) with optimal consumption, there is a similarly increasing course over the accelerator pedal travel. The computer determines the gear ratio required for the respective driving speed from the driver's desired performance with the accelerator pedal travel. In order to enable rapid power delivery, it is only sufficient in special cases, and then significantly less than before, for example when the accelerator pedal is withdrawn during a winding uphill ride, to increase the engine speed above the consumption-optimal range. The instantaneous increase to the maximum torque according to the invention ensures that the power is developed for small accelerator pedal movements even from consumption-optimized speeds. In the event of foreseeable large jumps in performance, the driver can increase the engine speed by tapping the accelerator pedal shortly before the desired increase in performance. As a result, the engine can work with optimal efficiency over long periods. The dash-dotted line 2 shows a possible position of the inhibition threshold on the pedal travel path, the dashed line 3 shows, for example, a possible course of the increase in the pedal force P.

Fig. 2 shows in the engine map, the adaptive operating characteristic dashed largely verbrauchsoptimalem area. Only through the maximum increase in torque according to the invention, even with small accelerator pedal movements, is it possible to develop power directly from this map area. This enables a spontaneous power adjustment, for example, for the current speed corrections when driving in a column. Without the extreme torque increase according to the invention, the adaptive operating characteristic curve would have to run much lower, in the area with higher specific consumption.

According to the invention, the computer increases the engine torque when the accelerator pedal is moved Starting point A immediately to the maximum possible torque. At the same time, the computer the transmission ratio increases. The new accelerator pedal position is already at point B. appropriate power is achieved, the engine torque is now continuously reduced, while the engine speed remains the same along the Power hyperbole increases up to point C of the adaptive operating characteristic.

On a winding uphill ride, the adaptive operating characteristic lies after one Accelerator pedal withdrawal lower. When the accelerator pedal is pressed, the computer increases the torque immediately from E to F. In F the engine power is immediate, even before a change in Gear ratio increased by 33%. Then along the performance hyperbola according to G only the speed increased at constant power. The performance increase from E to F is just as spontaneously as with a multi-step transmission.

In FIGS. 3 to 6 into the fuel consumption map is a direct injection diesel engine a dashed line, connecting the points with the minimum consumption for the respective power located. The right-hand scale shows the speed that the power specified on the left requires when driving stationary on a horizontal road and when there is no wind.

Fig. 3 shows h for a desired vehicle acceleration of 80 km to 120 /, for example at a motorway, the increase in the engine power according to an accelerator operation. When driving economically, the driver will preferably simply depress the accelerator pedal up to the inhibition threshold. The engine power increases immediately with the pedal actuation from point A to point 4 and already reaches point 5 in about 2 seconds, the absolute best fuel consumption in the engine map with approx. 27 kW. The entire acceleration process then takes place with this optimal engine efficiency. The accelerator can be forced as shown in FIG. 4 by tapping the accelerator pedal in advance . Once the desired speed has been reached and the driver releases the accelerator pedal, the computer immediately reduces the engine torque accordingly until the corresponding speed change has been reached and the engine is again operating at high torque to optimize consumption.

With the accelerator pedal, the driver can also use larger or smaller engine outputs for the Select acceleration process. The engine is always from the computer - with Exception of the first seconds - during the whole acceleration process on that for desired performance, controlled consumption-optimized torque. From a certain minimum speed applies to all driving conditions.  

Fig. 4 shows how in the lower speed range by tapping the accelerator pedal by changing the gear ratio, the engine speed from the starting point A, at 40 km / h is raised to point 6 prematurely. At the same time, the computer temporarily lowers the engine torque to such an extent that the engine power remains unchanged for the time being. A high engine output, for example the best fuel consumption point 7 in the map, is then immediately available to the driver for the acceleration process at the point in time suitable for the overtaking process.

In the previously described, optimally fuel-saving acceleration processes, the engine largely operates at constant speed during vehicle acceleration. The acceleration processes therefore do not have the usual acoustic accompanying picture in which the engine speed increases audibly with the driving speed. Those drivers who do not want to do without the accompanying music of the engine familiar from manual gearboxes and prefer a brisk driving style can fulfill this wish with an embodiment variant as illustrated in FIG. 5.

If, according to Fig. 5 the threshold is acceleration slightly exceeded the accelerator pedal path before or during a Fahrzeugbe, the computer, the transmission gear from reaching the preselected with the accelerator pedal engine speed (z. B. Item 9) also selectively retain constant. The engine speed is thus coupled to the increase in driving speed during the subsequent acceleration. The engine power increases with the engine speed and acceleration is accelerated. The engine speed is always at least equal to or greater than the engine speed specified with the accelerator pedal. After the accelerator pedal is withdrawn, the original control of the transmission ratio or engine speed according to the accelerator pedal position applies again. When the accelerator pedal is withdrawn, the engine torque is temporarily reduced so that the power is reduced to the power that corresponds to the new accelerator pedal position already during the speed reduction.

In the case of positive accelerator pedal movements, the engine torque is increased to the maximum possible, corresponding to the new accelerator pedal position, quickly, often before and during the change in gear ratio, by increasing the engine torque. The power curve from A to point 10 shown in FIG. 6 clearly shows this. The same applies to the reduction in output when the accelerator pedal is withdrawn, cf. the performance curve from A to 11 . The "suspender effect" previously objected to in CVT transmissions is largely eliminated as a result of this and by the possibility of prematurely increasing the engine speed by "tapping" the accelerator pedal, "the vehicle rather depends very well on the gas".

This method of controlling the drive train ensures a continuous Consumption-optimized engine efficiency, as with a consumption-oriented one Control characteristic a good power delivery is possible. Just before the driver will predict the necessary major increases in performance by tapping the Accelerator pedal raise the engine speed to areas that are not fuel-efficient.  

Likewise, the computer only backs up with frequent accelerator pedal movements, preferably with winding mountain routes, the spontaneous performance development by according to the state technology reduces the speed a little less when the accelerator pedal is withdrawn. The assignment of the Engine power to the accelerator pedal positions always remains constant.

The inhibition threshold on the fahlpedalweg causes or educates the driver to an optimal level for the first time economical and preferably in city traffic - due to the lower noise level - too particularly environmentally friendly driving style. In total, CVT gearboxes are used with this Control algorithm a similar order of magnitude of consumption reduction can be realized as in the transition from TD to TDI.

For the sake of completeness it should be mentioned that for the realization of the individual units, such as Setpoint generator, inhibitor threshold generator, as well as for the implementation of the individual computer Techniques known per se can be used as analyzes, in particular in WO 89/03329 and EP 0 663 155 A are explained; so that a more detailed Description of this can be omitted.

Claims (10)

1. Method for controlling a drive train of a motor vehicle with an internal combustion engine, with a continuously variable transmission and with an accelerator pedal to which a setpoint generator is assigned, in which method accelerator pedal movement sequences are monitored with the setpoint generator and analyzed in a computer to which a memory is assigned, whereby the driver and situation-related adaptation of the driving program also takes place, characterized in that the motor is brought to a progressive increase in engine power corresponding to the accelerator pedal position with the aid of the computer after each positive accelerator pedal movement, by the engine if there is no traction control intervention , is immediately controlled to the torque with which the engine power determined by the accelerator pedal travel is achieved as far as possible, even at the current engine speed, and the gear ratio is then calculated by the computer according to the respective driving speed speed is improved so that the engine power defined by the accelerator pedal position is achieved with the optimal engine speed stored in the driving program for this power, the engine speed only in special situations, for example by the driver and situation-related adaptation of the driving program. B. after an accelerator pedal retraction on a winding mountain ride, is raised substantially above the consumption-optimized engine speed, the engine output then still being fixed by the accelerator pedal position. 2. The method according to claim 1, characterized in that even with a small positive accelerator pedal movement using the computer immediately before the engine torque and briefly during the transmission change triggered by the accelerator pedal movement if necessary, increase to the maximum possible engine torque so that the Level of performance already during the translation change as much as possible the new one Pedal position with the later higher speed and then again the optimal consumption Torque corresponds. 3. The method according to claim 1 or 2, characterized in that at one If the accelerator pedal is withdrawn by the computer, the engine torque immediately, already during the gear ratio change triggered by this accelerator pedal movement, short-term so far is lowered that the smaller, corresponding to the selected new accelerator pedal position Engine power has already been reached during the change in gear ratio.   4. The method according to any one of claims 1 to 3, characterized in that the computer a short press on the accelerator pedal as a precautionary, desired by the driver The maximum value of the accelerator pedal movement corresponding engine speed increase is recognized and the Gear ratio is controlled accordingly, but the engine torque is lowered so far that the engine power remains unchanged for the time being at to accelerate later to avoid wasting time on revving up the engine and one secure immediate full acceleration. 5. The method according to any one of claims 1 to 4, characterized in that the driver by signals, preferably tactile signals on the accelerator pedal, an unfavorable engine efficiency is indicated by too high engine speed, these signals as soon as the longest Gear ratio is reached, or if a special driving condition, such as a Ascent with constantly changing power requirements, is determined, suppressed. 6. The method according to any one of claims 1 to 5, characterized in that those Engine speed, which enables the optimum consumption, by an inhibition threshold on Accelerator pedal travel is displayed, with the choice of this pedal position especially for everyone Acceleration processes the engine runs in the best range. 7. The method according to any one of claims 1 to 6, characterized in that one associated increasing brake pedal or brake fluid pressure increasing engine speeds and this from the computer, unless occasionally from the anti-lock braking system (ABS) prevented from being controlled by appropriate choice of translation. 8. The method according to any one of claims 1 to 7, characterized in that at As a precautionary measure, the driver makes brief pressure increases on the brake pedal if one any existing ABS does not intervene, the computer changes the translation is triggered to increase the engine speed. 9. The method according to any one of claims 1 to 8, characterized in that when a minimum speed, for example 35 km / h, is exceeded when the throttle is at zero Accelerator pedal an overrun cutoff always remains effective and the computer to minimize Drag losses, due to the corresponding gear ratio, the engine speed as far as possible lowered. 10. The method according to any one of claims 1 to 9, characterized in that if provided a cruise control system through this at low speeds, for example under 75 km / h, the drive is optimally switched on and off intermittently so that the Speed only a predetermined value, for example 2-5 km / h, over or is undercut.